Pressure control valves (such as pendulum valves and butterfly valves) used in vacuum chambers are often subject to a build-up of process gas contaminants on the vacuum wetted surfaces. These valves typically operate with very small clearances, so that when depositions occur on the valve surfaces, the motion of the valves is restricted. Typically, in these applications the valves use motors that deliver a higher torque, so that the motor can plow through the deposition while avoiding stepper motor slip, i.e. the inability to achieve the desired valve position. If a servo motor is utilized, rather than a stepper motor, the symptoms resulting from deposition buildup include the inability to maintain or achieve position setpoint.
Typically, users of the valves in these environments heat the valves to prevent deposition, i.e. to prevent condensation of process gasses. This is not always effective, however. Also, users of these valves in these environments typically perform a preventative maintenance (PM) cleaning of the valves, at certain time intervals. The PM generally involves removing the valve from the tool or vacuum chamber, and cleaning the valve mechanically or with a solvent. Because this cleaning causes tool downtime, it is performed as infrequently as possible. It is difficult to predict when the PM is needed, however, so the PM interval may result in being too short, causing excessive maintenance cost, or too long, causing valve and pressure control problems affect wafer production.
For these reasons, it would be desirable to be able to predict the need for cleaning valve systems, without relying on arbitrary PM intervals.